The dGPU opt-in you are referring to is already implemented in the official release for 64-bit Windows.
Unfortunately, there is no way to enable this feature from pure Java code. To overcome this, the official release uses the Groan Autodeployer, which is an executable wrapper that is able to enable the switch in native code before starting the Java Virtual Machine. The Groan Autodeployer is available on my SourceForge profile if you want to set this up yourself. But, the documentation and configuration is not very user friendly and please understand I do not offer technical support for this.
There are other Java executable wrappers you can try which have better documentation. I have never seen one that has the dGPU opt-in, but they do play nicer with Nvidia Optimus (e.g. you can configure the executable separately in the Nvidia control panel, or if you have a somewhat recent driver you can right click on the executable to select the GPU).
Without creating a native executable I think the only way to use the dGPU is to set the java executable itself to use the dGPU in the Nvidia control panel. In my experience this will work if you select the correct version of the executable, but I understand it's not a very nice solution.